public IPolygon bufferFromWebGeometry(WebGeometry webGeom, double bufferDist) {
    AGSLocalMapResource resource = (AGSLocalMapResource) this
        .getContextMgrOnRender().getResources().get("Basemap");

    IServerContext servercontext = resource.getServerContext();

    com.esri.arcgisws.Geometry agsGeom = (com.esri.arcgisws.Geometry) AGSUtil
        .toAGSGeometry(webGeom);

    IGeometry pGeom = (IGeometry) AGSUtil.createArcObjectFromStub(agsGeom, this
        .getServerContext());
    try {

      System.out.println(pGeom.getEnvelope().getXMax() + ","
          + pGeom.getEnvelope().getYMax());

      ITopologicalOperator p, u;

      p = new ITopologicalOperatorProxy(pGeom);
      IPolygon polygon = (IPolygon) p.buffer(bufferDist); // Exception Thrown
      u = new ITopologicalOperatorProxy(polygon);
      IPolygon bufferPolygon = (IPolygon) u.union(polygon);

      return bufferPolygon;
    } catch (IOException e) {
      e.printStackTrace();
      return null;
    }
  }

WebPolygon webPoly = new WebPolygon();
					
					int increment = 10;
					double x = 0.0;
					double y = 0.0;

//**** 
//maybe this is difference on your code
					PointN clrPnt = new PointN();
					//WebPoint clrPnt = new WebPoint();
					WebRing wr = new WebRing();
					for (int p = 0; p <= 360; p=p+increment) {
						x = centerPnt.getX() + (dist * Math.cos(p*Math.PI/180));
						y = centerPnt.getY() + (dist * Math.sin(p*Math.PI/180));

						clrPnt.setX(x);
						clrPnt.setY(y);
						
						//convert from ws to web point and add to ring
			WebPoint webPnt = (WebPoint)AGSUtil.fromAGSGeometry(clrPnt);
						
						wr.addPoint(webPnt);
					
					}			
					webPoly.addRing(wr);

WebGeometry webGeometry;
		IGeometry buffer;
		IServerContext serverContext;
		IMapServerObjects imapServerObject;
		int featureCounter;
		RectangleToolService rectangleToolService=new RectangleToolService();
		String errorMessage="";
		try {

			WebQuery webQuery=webContext.getWebQuery();
			if(units.compareTo(bundle.getString("kilometers"))==0)
			{
				bufferDistance=bufferDistance*1000;
			}           
			AGSLocalMapResource resource = (AGSLocalMapResource) webContext.getResources().get(aGSLocalMapResourceName);
			serverContext = (IServerContext) resource.getServerContext();			
			imapServerObject=resource.getLocalMapServer();					
			ILayer iLayer = imapServerObject.getLayer(resource.getMapName(),activeLayer);

			IFeatureLayer iFeatureLayer = new IFeatureLayerProxy(iLayer);


			IPolygon polygon =null;
			for(featureCounter=0; featureCounter<selectedFeatures.length; featureCounter++)
			{


				IFeature iFeature = iFeatureLayer.getFeatureClass().getFeature(selectedFeatures[featureCounter]);
				ITopologicalOperator p = new ITopologicalOperatorProxy(iFeature.getShape());
				
				System.out.println("iFeature.getShape():::"+iFeature.getShape().getGeometryType());
				
				
				buffer = p.buffer(bufferDistance); // Assumes a Geographic projection, for simplicity.

				polygon = new IPolygonProxy(buffer);

				polygon.setSpatialReferenceByRef(buffer.getSpatialReference());

				String soapString = com.esri.adf.web.ags.util.AGSUtil.serializeArcObject(polygon,serverContext);
				soapString = soapString.replaceAll("xsi:type=\"soapenc:Array\"", "");
				PolygonN polygonN=(PolygonN)AGSUtil.deserializeStub(soapString,PolygonN.class);	


				SpatialFilter spatialFilter = new SpatialFilter();
				spatialFilter.setSpatialRel(EsriSpatialRelEnum.esriSpatialRelIntersects);
				spatialFilter.setWhereClause("");
				spatialFilter.setSearchOrder(EsriSearchOrder.esriSearchOrderSpatial);
				spatialFilter.setSpatialRelDescription("");
				spatialFilter.setGeometryFieldName("");
				spatialFilter.setFilterGeometry(polygonN);

				errorMessage = rectangleToolService.queryRectangleBuff(webContext,spatialFilter,targetLayer,"Features for id: "+selectedFeatures[featureCounter],aGSLocalMapResourceName,agsMapFunctionalityName);		
				webGeometry=AGSUtil.fromAGSGeometry(polygonN);
				if(webGeometry!=null){
					webQuery.addDisplayGeometry(webGeometry);
				}
				webContext.refresh();
			 }
			
		}